1. Field of the Invention
The present invention relates to a method for manufacturing a side panel.
2. Related Art
According to a press working method, various kinds of products having various shapes can be manufactured by a relatively simple process. Accordingly, the press working method has been widely utilized in many fields. When the press working method is utilized, basically, a single sheet of material, for example, a metal plate is used for a single kind of products.
However, there is a case where an area of a portion to be punched out by a press working is too wide or a shape, a material quality and a sheet pressure of a product to be obtained is special. In such a case, there is a problem that a proportion of waste material out of a material to be pressed highly increases and a yield ratio of the material is lowered. In this regard, JP-A-59-220229 discloses a processing method in which a plurality of members to be pressed are combined and integrally welded, and then press-worked to obtain a final product.
Further, in an automobile industry required for a mass production, a tailor welded blank method in which materials having desired properties are placed on desired regions has been adapted. According to the tailor welded blank method, materials which have a desired material quality and sheet thickness different from each other can be combined as a blank material. Then, the combined blank material is integrally formed by a welding and press-worked by a press machine to obtain a final product. By doing so, a desired press working can be performed by single press working.
However, when the tailor welded blank method is adapted, the problem is as follows. Regarding to this problem, a case of manufacturing a side panel in a vehicle will be described as an example by referring to FIG. 4 and FIG. 5.
A side panel 300 illustrated in FIG. 4 includes an upper member 100 and a lower member 200 which have strengths different from each other. In the side panel 300 illustrated in FIG. 4, the upper member 100 includes a front pillar portion 101, a loop pillar portion 102 and a rear pillar portion 103. Meanwhile, the lower member 200 is constituted by a side sill which extends from a lower side of the side panel 300 to a rear fender. The side sill includes a side sill front portion 201 connected to the lower side of the side panel 300, a side sill main portion 202 and a side sill rear portion 203 connected to the front pillar portion 103 and a wheel portion of the rear fender.
Generally, the upper member 100 of the side panel 300 is considered as a part having a focus on design. For this reason, the upper member is made of a relatively soft material to obtain good formability. Meanwhile, the lower member 200 of the side panel 300 is made of a material which has a higher strength than the upper member 100 in order to obtain to a safety during driving or collision.
The upper member 100 and the lower member 200 of the side panel 300 are joined to each other by welding a joined part A between the rear pillar portion 101 and the side sill front portion 201 and a joined part B between the front pillar portion 103 and the side sill rear portion 203.
A material of the lower member 200 of the side panel 300 has a higher strength than a material of the upper member 100 of the side panel 300. Accordingly, when the material of the upper member 100 and the material of the lower member 200 of the side panel 300 are press-worked, it is necessary to apply higher press load on the material of the lower member 200 having a high strength than the material of the upper member 100.
Meanwhile, if the material of the side panel 300 is press-worked while being placed on a press machine in a state where a center portion of the press area is positioned near a center portion of the material of the side panel 300, the material of the lower member 200 required for a high press load is arranged at a position offset downward from the press machine. For this reason, when the material of the upper member 100 and the material of the lower member 200 of the side panel 300 are simultaneously press-worked, a bias is caused in the press load and therefore a processing surface of a mold forming a press surface is inclined. Consequently, there is a problem which a suitable press working cannot be achieved for the side panel 300.
For this reason, although the man hour increases, in order to securely perform the press working, the metal plate 100A of the upper member of the side panel 300 and the metal plate 200A of the lower member of the side panel 300 are subjected to a drawing work by a separate press machine and then processed metal plates 100B, 200B are shaped, as illustrated in FIG. 5. Subsequently, the processed metal plates 100B, 200B are further press-worked by a separate press machine to allow unnecessary portions thereof to be removed. By these processes, the upper members 100-1 to 100-n and the lower members 200-1 to 200-n are formed. The upper member 100 and the lower member 200 of the side panel 300 thus formed are joined to each other at the joined parts A, B using a spot welding and therefore the side panel is completed as a product.
It is theoretically not impossible to press-work a material of the upper member 100 and a material of the lower member 200 having a strength different from the material of the upper member at one time by single press machine. For example, when a metal plate having a high press load and a normal metal plate are simultaneously press-worked, it is enough to cause the press machine to apply a sufficient high press load to ignore the strength difference between pluralities of metal plate having strengths different from each other. However, in this case, since the load pressure of the press machine significantly increases and a large press machine is required, this is not economical.